Base oil for cooling of device, device-cooling oil containing the base oil, device to be cooled by the cooling oil, and device cooling method using the cooling oil

ABSTRACT

A device-cooling base oil includes 30 mass % of at least one of an oleyl ester (e.g., oleate and oleyl alcohol ester) and oleyl ether. The oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch. The base oil has a kinematic viscosity at 40 degrees C. in a range of 4 mm 2 /s to 30 mm 2 /s. A device-cooling oil provided by blending the base oil is excellent in electrical insulation properties and thermal conductivity, and thus is favorably usable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle, a hybrid vehicle or the like.

TECHNICAL FIELD

The present invention relates to a base oil for cooling a device, adevice-cooling oil using the base oil, a device to be cooled by thedevice-cooling oil, and a device cooling method using the device-coolingoil.

BACKGROUND ART

An improvement in the performance of electric vehicles and hybridvehicles results in an increase in the power density and, consequently,the heat generation of a motor. Accordingly, coil, magnet and the likehave been improved in heat resistance and, further, a variety ofmodifications in motor design have been made for, for instance, reducingthe increased heat generation resulting from the improved performance ofa motor.

For cooling a motor, there have been suggested three types of methods,i.e., an air-cooling method, a water-cooling method and an oil-coolingmethod. Among the above, the air-cooling method advantageously does notrequire any specific coolant to be prepared, but is unlikely to providea large cooling capacity. The water-cooling method is excellent incooling properties because water exhibits a high thermal conductivity.However, since a motor coil cannot be directly cooled because of theelectrical conductivity of water, a cooling pipe has to be laid out,which, disadvantageously, increases the size of a cooling device.

As compared with the above cooling methods, the oil-cooling method usesoil, which is excellent in cooling efficiency and low in electricalconductivity, so that the oil-cooling method enables directly cooling amotor, resulting in a compact design. Additionally, when lubrication ofa rotary member is simultaneously required, an oil for cooling the motoris usable as a dual-purpose oil not only for cooling but also forlubrication (i.e., the same packaging). For instance, hybrid vehicles inpractice use a mechanism for circulating a transmission oil tosimultaneously cool a motor. Some wheel-driving motors for electricvehicles have been modified in design such that a lubricating oil iscirculated not only for lubricating a planetary gear but also forcooling a motor coil.

As such a dual-purpose oil usable for cooling a motor while lubricatinga transmission or the like, there has been suggested, for instance, alubricating oil composition provided by blending a low-viscosity mineraloil or synthetic oil with at least one of (A) zinc dithiophosphatecontaining a hydrocarbon group, (B) triaryl phosphate and (C) triarylthiophosphate (see Patent Literature 1). Additionally, as thedual-purpose oil, there have been suggested: a lubricating oilcomposition using a base oil that has a urea adduct value of 4 mass % orless, a kinematic viscosity of 25 mm²/s or less at 40 degrees C. and aviscosity index of 100 or more, the lubricating oil composition having aheat transfer coefficient of 720 W/m²·degrees C. or more (see PatentLiterature 2); and a lubricating oil composition using a base oil thatcontains an ester synthetic oil of 10 mass % to 100 mass % of the totalamount of the base oil and has a kinematic viscosity of less than 15mm²/s at 40 degrees C., a viscosity index of 120 or more and a densityof 0.85 g/cm³ or more at 15 degrees C., the lubricating oil compositionhaving a heat transfer coefficient of 780 W/m²·degrees C. or more (seePatent Literature 3). Each of Patent Literatures 1, 2 and 3 disclosesthat the suggested lubricating oil composition is excellent inelectrical insulation properties, cooling properties and lubricity andis favorably usable for electric motor vehicles such as electricvehicles and hybrid vehicles.

CITATION LIST Patent Literature(s)

-   Patent Literature 1: WO2002/097017-   Patent Literature 2: JP-A-2009-161604-   Patent Literature 3: JP-A-2009-242547

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In connection with the cooling properties of the lubricating oilcomposition, Patent Literature 1 does not teach anything but loweringthe viscosity of the lubricating oil composition, and does not even showdata on cooling properties. Additionally, neopentylglycol 2-ethylhexanoic acid diester and alkylbenzene, which are used as base oils inExamples of Patent Literature 1, are unlikely to exhibit excellentcooling properties because of their poor thermal conductivity. PatentLiterature 2 teaches in paragraph [0020] that “as an urea adduct, . . .a component that deteriorates thermal conductivity . . . is accuratelyand reliably collected.” In other words, contrarily to the fact, PatentLiterature 2 teaches that a urea adduct component deteriorates thermalconductivity. It is probably wrong that “a component having a longparaffin main chain exhibits a poor thermal conductivity.” In view ofthe above, it is doubtful whether or not Patent Literature 2 discloses alubricating oil composition excellent in cooling properties. Estercompounds specifically disclosed in Patent Literature 3 are azelaic aciddi-2-ethylhexyl, neopentyl glycol 2-ethylhexanoate diester and2-ethylhexyl oleate, which unfavorably exhibit a low thermalconductivity.

An object of the invention is to provide: a base oil having excellentelectrical insulation properties and thermal conductivity for cooling adevice; a device-cooling oil using the base oil; a device to be cooledby the device-cooling oil; and a device cooling method using thedevice-cooling oil

Means for Solving the Problems

As a measure of the cooling properties of a fluid, “heat transfercoefficient (heat transfer amount per unit area, unit temperature andunit time)” is usable. A fluid having a higher value of heat transfercoefficient exhibits better cooling properties. Since heat transfercoefficient is not physical properties but is variable depending onconditions such as flow rate and material type, modifications in designfor increasing heat transfer coefficient have been made.

For increasing heat transfer coefficient by modifications in terms of afluid, it should be noted that since heat transfer coefficient isvariable in relation to Nusselt number, Reynolds number and Prandtlnumber, the cooling properties of a fluid are affected by the physicalproperties of the fluid such as kinematic viscosity, thermalconductivity, specific heat and density. Specifically, a fluid havingsmaller kinematic viscosity but larger thermal conductivity, specificheat and density exhibits better cooling properties. Accordingly, it hasbeen considered to lower the viscosity of a fluid (e.g., a lubricatingoil) for improving the cooling properties thereof. However, when theviscosity of a lubricating oil is lowered, the cooling properties areimproved but a sufficient film thickness of the lubricating oil cannotbe provided, thereby causing lubrication failure. In view of the above,the minimum viscosity is determined depending on conditions regarding aportion to be lubricated in a transmission or the like. Thus, amonglubricating oils having the same kinematic viscosity, one having largerthermal conductivity, specific heat and density has better coolingproperties. For instance, a heat transfer coefficient during forcedconvection of a plate having a uniform temperature is proportional tothe thermal conductivity to the power of two thirds, the specific heatto the power of one third and the density to the power of one third, sothat the heat transfer coefficient is the most affected by the thermalconductivity.

In view of the above, a base oil having a high thermal conductivity isfavorable for a cooling oil usable in a device such as a motor. However,a correlation between the molecular structure and the thermalconductivity of a base oil has not been studied. Regarding basiclow-molecular compounds, there is only a small amount of informationavailable. Specifically, alcohols such as glycerin, ethyleneglycol andmethanol are excellent in thermal conductivity as described in KagakuBinran (“Handbook of Chemistry”). However, polar compounds such asalcohols exhibit a poor volume resistivity (poor electrical insulationproperties), so that they are not usable as a cooling oil for directlycooling a device such as motor. Additionally, they are not expected tobe usable as a lubricating oil because of a lack of lubricity.

As a result of concentrated studies in terms of molecular design, theinventor has found that a compound having a predetermined molecularstructure is excellent in cooling properties, electrical insulationproperties and lubricity.

In other words, according to the invention, there are provided: a baseoil for cooling a device; a device-cooling oil using the base oil; adevice to be cooled by the device-cooling oil; and a device coolingmethod using the device-cooling oil, as described below.

(1) A base oil for cooling a device includes 30 mass % or more of atleast one of an oleyl ester (oleate and an oleyl alcohol ester) and anoleyl ether, in which the oleyl ester and the oleyl ether each have 23or more of a total number of a terminal methyl group, a methylene groupand an ether group in a main chain, the oleyl ester and the oleyl ethereach have 1 or less of a total number of a methyl branch and an ethylbranch, and the base oil has a kinematic viscosity in a range of 4 mm²/sto 30 mm²/s.(2) In the above base oil, the oleyl ester and the oleyl ether arecontained at 50 mass % or more.(3) A base oil for cooling a device contains 30 mass % or more of atleast one of an aliphatic monoester and an aliphatic monoether, in whichthe aliphatic monoester and the aliphatic monoether each have 18 or moreof a total number of a terminal methyl group, a methylene group and anether group in a main chain, the aliphatic monoester and the aliphaticmonoether each have 2 or less of a total number of a methyl branch andan ethyl branch, and the base oil has a kinematic viscosity in a rangeof 4 mm²/s to 30 mm²/s.(4) In the above base oil, at least one of the aliphatic monoester andthe aliphatic monoether has a chain structure.(5) A base oil for cooling a device contains 30 mass % or more of atleast one of an aliphatic diester and an aliphatic diether, in which thealiphatic diester and the aliphatic diether each have 20 or more of atotal number of a terminal methyl group, a methylene group and an ethergroup in a main chain, the aliphatic diester and the aliphatic diethereach have 2 or less of a total number of a methyl branch and an ethylbranch, and the base oil has a kinematic viscosity in a range of 4 mm²/sto 30 mm²/s.(6) A base oil for cooling a device contains 30 mass % or more of atleast one of an aliphatic triester, an aliphatic triether, an aliphatictri(etherester), an aliphatic tetraester, an aliphatic tetraether, analiphatic tetra(etherester), an aromatic diester, an aromatic dietherand an aromatic di(etherester), wherein each of the esters, the ethersand the etheresters has 18 or more of a total number of a terminalmethyl group, a methylene group and an ether group in a main chain and 1or less of a total number of a methyl branch and an ethyl branch, andthe base oil has a kinematic viscosity in a range of 4 mm²/s to 30mm²/s.(7) In the above base oil, a thermal conductivity of the base oil at 25degrees C. is 0.142 W/(m·K) or more.(8) In the above base oil, a volume resistivity of the base oil at 25degrees C. is 10¹⁰ Ω·cm or more.(9) A device-cooling oil contains the above base oil.(10) A device is configured to be cooled by the device-cooling oil.(11) The above device is usable for an electric vehicle or a hybridvehicle.(12) The device is at least one of a motor, a battery, an inverter, anengine and an electric cell.(13) A device cooling method uses the device-cooling oil.

A device-cooling oil provided by blending a base oil for cooling adevice according to the invention is excellent in electrical insulationproperties and thermal conductivity, and thus is favorably usable forcooling a motor, a battery, an inverter, an engine, an electric cell orthe like in an electric vehicle, a hybrid vehicle or the like.

DESCRIPTION OF EMBODIMENT(S)

A device-cooling base oil, a device-cooling oil containing thedevice-cooling base oil, a device to be cooled by the device-coolingoil, and a device cooling method using the device-cooling oil accordingto exemplary embodiments of the invention will be described below.

First Exemplary Embodiment

A device-cooling base oil in a first exemplary embodiment of theinvention (hereinafter referred to as a “base oil”) contains at leastone of an oleyl ester (i.e., an oleate, an oleyl alcohol ester) and anoleyl ether as a basic component.

The oleyl ester and the oleyl ether each have 23 or more of a totalnumber of a terminal methyl group, a methylene group and an ether groupin a main chain and 1 or less of a total number of a methyl branch andan ethyl branch in a molecule. The “main chain” herein means a portionhaving the longest chain structure in the molecule.

The first exemplary embodiment will be described in detail below.

For improving the thermal conductivity of liquid molecules, it isimportant to accelerate the transfer of thermal vibration energyresulting from collision between the molecules and to design themolecules such that the vibration energy is not dispersed in themolecules. In order to increase the frequency of collision between themolecules, it is effective to elongate the main chain of each molecule,thereby increasing the movable range of the molecule end based on arotation around at a carbon-carbon bond. Specifically, in order to keepthe vibration energy being concentrated in the main chain of eachmolecule without dispersing in the molecule, methyl branch and ethylbranch, which are short in length and cause dispersion of the vibrationenergy, are decreased in number. Additionally, the methyl group and theethyl group are not favorable for collision with the adjacent molecules(energy transfer) because of a small movable range thereof. Esters andethers having a long chain structure are recognized as a molecule havingsuch a structure.

Accordingly, in the exemplary embodiment, a main component of a base oilis provided by an oleyl ester or an oleyl ether in which the totalnumber of a terminal methyl group(s), a methylene group(s) and an ethergroup(s) in the main chain is 23 or more and the total number of amethyl branch and an ethyl branch in the molecule is 1 or less. Thenumber of the methylene group in the oleyl ester and the oleyl ether ispreferably 22 or more, more preferably 24 or more in terms of anenhancement of cooling properties.

Each entire structure of the oleyl ester and the oleyl ether ispreferably a chain structure, more preferably a straight-chainstructure, in terms of an enhancement of the cooling properties of thebase oil.

Such an oleyl ester is obtainable by typically known methods ofmanufacturing esters. A method of manufacturing the oleyl ester issubject to no limitation. For instance, the oleyl ester is obtainableby: a dehydration condensation reaction between oleic acid and alcoholor a dehydration condensation reaction between carboxylic acid and oleylalcohol; a condensation reaction between oleic acid halides and alcoholor a condensation reaction between carboxylic acid halides and oleylalcohol; and an ester exchange reaction. For instance, alcohol (thestarting material) having a long linear alkyl chain and carboxylic acid(the starting material) having a long linear alkyl chain are preferablyused for synthetic reaction such that the total number of the terminalmethyl group, the methylene group and the ether group in the main chain(i.e., the longest chain in a molecule) is 23 or more and the totalnumber of a short alkyl side chain in the molecule (i.e., the methylbranch and the ethyl branch) is 1 or less.

Examples of the carboxylic acid (the starting material) includemonocarboxylic acids such as oleic acid, n-hexanoic acid, n-heptanoicacid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoicacid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid,ethylhexanoate, butyl octanoic acid, pentyl nonanoic acid, hexyldecanoic acid, heptyl undecanoic acid, octyldodecanoic acid, methylheptadecanoic acid and benzoic acid.

Examples of the alcohol (the starting material) include oleyl alcohol,n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol,n-dodecanol, n-tridecanol, n-tetradecanol, ethylhexanol, butyloctanol,pentylnonanol, hexyldecanol, heptylundecanol, octyldodecanol,methylheptadecanol, benzyl alcohol, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monopropyl ether,ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monopropyl ether,diethylene glycol monobutyl ether, triethylene glycol monomethyl ether,triethylene glycol monoethyl ether, triethylene glycol monopropyl etherand triethylene glycol monobutyl ether.

A catalyst such as titanium tetraisopropoxide may be used anesterification catalyst, or no catalyst may be used.

The above oleyl ether may be manufactured by a typical ethermanufacturing method such as the Williamson ether synthetic method, butthe manufacturing method of the oleyl ether is subject to no limitation.

The base oil of the exemplary embodiment contains 30 mass % or more ofat least one of the ester and the ether described above, preferably 50mass % or more, more preferably 60 mass % or more, further preferably 70mass % or more, particularly preferably 80 mass % or more. When the baseoil contains the ester and the ether at less than 30 mass %, the baseoil may not exhibit a sufficient cooling properties. It should be notedthat a base oil for cooling a device may be provided only by the baseoil of the exemplary embodiment (at 100 mass %).

The base oil of the exemplary embodiment has a kinematic viscosity at 40degrees C. in a range from 4 mm²/s to 30 mm²/s, preferably from 4 mm²/sto 20 mm²/s. If the kinematic viscosity of the base oil at 40 degrees C.is less than 4 mm²/s, for instance, when the base oil is used as adual-purpose oil not only for a motor but also for a transmission or thelike, the base oil may exhibit an insufficient lubricity. On the otherhand, if the kinematic viscosity of the base oil at 40 degrees C.exceeds 30 mm²/s, the cooling properties may be insufficient.Additionally, when such a base oil is used as a cooling oil for a motoror the like, the cooling oil is unlikely to smoothly circulate within asystem or the like.

The base oil of the exemplary embodiment preferably has a thermalconductivity at 25 degrees C. of 0.142 W/(m·K) or more, more preferably0.144 W/(m·K) or more, in terms of the cooling properties.

The base oil of the exemplary embodiment preferably has a volumeresistivity at 25 degrees C. of 10¹⁰Ω·cm or more, more preferably 10¹¹Ω·cm or more, further preferably 10¹²Ω·cm or more, particularlypreferably 10¹³ Ω·cm or more.

The base oil of the exemplary embodiment may be provided by blending theabove-mentioned ester and ether with an additional component (base oil).In this case, the additional component is not particularly limited intype. However, even after blending the additional component, theviscosity range, the cooling properties, the insulation properties andthe lubricity should be maintained as described above and the advantagesof the invention should be achieved.

Preferable examples of the additional component are a mineral oil and asynthetic oil. Examples of the mineral oil are a naphthenic mineral oil,a paraffinic mineral oil, a GTL mineral oil and a WAX-isomerized mineraloil. Specifically, the mineral oil is exemplified by a light neutraloil, a medium neutral oil, a heavy neutral oil and a bright stock, whichare provided by solvent refining or hydrogenation refining.

Examples of the synthetic oil are polybutene and a hydrogenated productthereof, poly-alpha-olefin (e.g., 1-octene oligomer and 1-deceneoligomer) and a hydrogenated product thereof, alpha-olefin copolymer,alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol,polyoxyalkylene glycol ester, polyoxyalkylene glycol ether, hinderedester, and silicone oil.

A device-cooling oil containing the base oil of the exemplary embodimentis favorably usable for cooling a motor, a battery, an inverter, anengine and an electric cell or the like in an electric vehicle, a hybridvehicle or the like. Since the viscosity of the base oil at 40 degreesC. is in the above predetermined range, the device-cooling oil isexcellent in lubricity, and thus is favorably usable as a dual-purposeoil not only for cooling but also for lubricating a planetary gear, atransmission or the like.

A variety of additives may be blended in the device-cooling oil of theexemplary embodiment as long as an object of the invention isattainable. For instance, a viscosity index improver, an antioxidant, adetergent dispersant, a friction modifier (e.g., an oiliness agent andan extreme pressure agent), an antiwear agent, a metal deactivator, apour point depressant, and an antifoaming agent can be blended asneeded. It should be noted that when the device-cooling oil is used as adual-purpose oil, the respective blending ratios of the additives shouldbe determined such that the device-cooling oil can exhibit lubricatingproperties while maintaining electrical insulation properties. In viewof the above, the respective blending ratios are preferably determinedsuch that the device-cooling oil has a thermal conductivity at 25degrees C. of 0.142 W/(m·K) or more, a volume resistivity at 25 degreesC. of 10¹⁰ Ω·m or more, and a kinematic viscosity at 40 degrees C. of 4mm²/s to 30 mm²/s.

Examples of the viscosity index improver are a non-dispersivepolymethacrylate, a dispersive polymethacrylate, an olefin copolymer(e.g., an ethylene-propylene copolymer), a dispersive olefin copolymer,and a styrene copolymer (e.g., a styrene-diene copolymer hydride). Whenthe dispersive or non-dispersive polymethacrylate is used as theviscosity index improver, the mass average molecular weight of theviscosity index improver is preferably in a range from 5,000 to 300,000.When the olefin copolymer is used, the mass average molecular weight ispreferably in a range from 800 to 100,000. One of these viscosity indeximprovers may be singularly blended or a combination thereof may beblended. The content of the viscosity index improver(s) is preferably ina range from 0.1 mass % to 20 mass % of the total amount of the coolingoil.

Examples of the antioxidant are: amine antioxidants such as alkylateddiphenylamine, phenyl-alpha-naphthylamine, and alkylatedphenyl-alpha-naphthylamine; phenol antioxidants such as2,6-di-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol),isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, andn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; sulfur-basedantioxidants such as dilauryl-3,3′-thiodipropionate; phosphorus-basedantioxidants such as phosphite; and molybdenum-based antioxidants. Oneof these antioxidants may be singularly blended or a combination thereofmay be blended. Preferably, two or more of these antioxidants areblended in combination and the content thereof is in a range from 0.01mass % to 5 mass % of the total amount of the cooling oil.

Examples of the detergent dispersant are: metal-based cleaners such asalkaline earth metal sulfonate, alkaline earth metal phenate, alkalineearth metal salicylate, and alkaline earth metal phosphonate; andashless dispersants such as alkenyl succinimide, benzylamine,alkylpolyamine, and alkenyl succinimide ester. One of these detergentdispersants may be singularly blended or a combination of two or morethereof may be blended. The content of the detergent dispersant(s) ispreferably in a range from 0.1 mass % to 30 mass % of the total amountof the cooling oil.

Examples of the friction modifier or the antiwear agent are: sulfurcompounds such as olefin sulfide, dialkyl polysulfide, diarylalkylpolysulfide, and diaryl polysulfide; phosphorus compounds such asphosphate, thiophosphate, phosphite, alkyl hydrogen phosphite, phosphateamine salt, and phosphite amine salt; chloride compounds such aschlorinated fat and oil, chlorinated paraffin, chlorinated fatty acidester, and chlorinated fatty acid; ester compounds such as alkyl oralkenyl maleate, and alkyl or alkenyl succinate; organic acid compoundssuch as alkyl or alkenyl maleic acid, and alkyl or alkenyl succinicacid; and organic metal compounds such as naphthenic acid salt, zincdithiophosphate (ZnDTP), zinc dithiocarbamate (ZnDTC), sulfurizedoxymolybdenum organophosphorodithioate (MoDTP), and sulfurizedoxymolybdenum dithiocarbamate (MoDTC). The content of the frictionmodifier or the antiwear agent is preferably in a range from 0.1 mass %to 5 mass % of the total amount of the cooling oil.

Examples of the metal deactivator are benzotriazole, triazolederivative, benzotriazole derivative, and thiadiazole derivative. Thecontent of the metal deactivator is preferably in a range from 0.01 mass% to 3 mass %.

Examples of the pour point depressant are an ethylene-vinyl acetatecopolymer, a condensate of chlorinated paraffin and naphthalene, acondensate of chlorinated paraffin and phenol, polymethacrylate, andpolyalkylstyrene, among which polymethacrylate is preferably usable. Thecontent of the pour point depressant is preferably in a range from 0.01mass % to 5 mass % of the total amount of the cooling oil.

As the antifoaming agent, a liquid silicone is suitable and,specifically, methylsilicone, fluorosilicone, polyacrylate and the likeare preferably usable. The content of the antifoaming agent ispreferably in a range from 0.0005 mass % to 0.01 mass % of the totalamount of the cooling oil.

Examples of First Exemplary Embodiment

Next, the first exemplary embodiment will be further described in detailbased on Examples, which by no means limit the first exemplaryembodiment.

Specifically, base oils shown in Table 1 were prepared and variousevaluations thereof were conducted. A preparation method and anevaluation method (a physical properties measuring method) for the baseoils are as follows.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Comp. 1 Comp. 2 Base Oil oleyl n-dodecyl n-octyl 16-n-octanoic n-octyloleyl butoxyethyl 2-ethylhexyl group-II (CompoundName) oleate oleate oleate methylheptadecyl acid oleyl ether oleateoleate purified oleate mineral oil Total of terminal methyl, 32 28 24 3124 24 23 21 mixture of methylene and ether in plural kinds main chainTotal of methyl and ethyl 0 0 0 1 0 0 0 1 mixture of branches inmolecule plural kinds Thermal Conductivity 0.153 0.149 0.146 0.149 0.1460.147 0.146 0.140 0.130 (25° C.) W/m · K Volume Resistivity 4.4E+113.6E+12 1.6E+11 1.5E+13 2.2E+11 2.4E+12 1.4E+10 2.9E+12 1.2E+15 (25° C.)Ω · cm Kinematic Viscosity 18.00 12.60 8.552 20.93 9.308 8.862 7.3168.331 9.898 (40° C.) mm²/s Kinematic Viscosity 5.018 3.765 2.837 5.2843.002 2.871 2.491 2.705 2.722 (100° C.) mm²/s Viscosity Index 232 213209 204 205 199 196 188 116 Density (15° C.) g/cm³ 0.8707 0.8661 0.86820.8693 0.8682 0.8419 0.8928 0.8690 0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus,oleic acid (127 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.), oleyl alcohol (145 g, a reagent manufactured by TokyoChemical Industry Co., Ltd.), mixed xylene (100 mL, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.), and titaniumtetraisopropoxide (0.1 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) were put. A reaction was conducted at 140 degrees C.for two hours while water was distilled away under nitrogen stream withstirring. Subsequently, the reaction product was washed with saturatedsaline three times and with 0.1 N aqueous sodium hydroxide three timesand was then dried with anhydrous magnesium sulfate (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.). After filtration ofmagnesium sulfate, excessive alcohol (the starting material) wasdistilled away to obtain oleyl oleate (215 g). This compound wasmeasured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density). The results are shown in Table 1. The results of thefollowing Examples and Comparatives are also shown in Table 1.

Example 2

Example 2 was performed in the same manner as in Example 1 except thatn-dodecyl alcohol (101 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that184 g of n-dodecyl oleate was obtained. This compound was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).

Example 3

Example 3 was performed in the same manner as in Example 1 except thatn-octyl alcohol (71 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.) was used in place of 145 g of oleyl alcohol, so that 162 g ofn-octyl oleate was obtained. This compound was measured in terms of thephysical properties thereof (i.e., thermal conductivity, volumeresistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that16-methylheptadecanol (147 g, product name: Isostearyl Alcohol EX,manufactured by KOKYU ALCOHOL KOGYO CO., LTD) was used in place of 145 gof oleyl alcohol, so that 16-methylheptadecyl oleate (212 g) wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Example 5

Example 5 was performed in the same manner as in Example 1 except thatn-octanoic acid (65 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.) and 107 g of oleyl alcohol were used in place of 127 g ofoleic acid and 145 g of oleyl alcohol, so that n-octanoic acid oleyl(143 g) was obtained. This compound was measured in terms of thephysical properties thereof (i.e., thermal conductivity, volumeresistivity, kinematic viscosity, viscosity index and density).

Example 6

To a 1-L glass flask, oleyl alcohol (107 g), 1-bromooctane (120 g, areagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutylammonium bromide (10 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.), and an aqueous sodium hydroxide (200 g, obtained bydissolving 60 g of sodium hydroxide in 140 g of water). A mixture wasreacted at 70 degrees C. for 20 hours with stirring. After the reaction,the reaction mixture was transferred to a separating funnel. An organicphase was washed five times with water (300 mL). Subsequently, theorganic phase was distilled, so that n-octyl oleyl ether (103 g) wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Example 7

Example 7 was performed in the same manner as in Example 1 except thatethylene glycol monobutyl ether (65 g, a reagent manufactured by TokyoChemical Industry Co., Ltd.) was used in place of 145 g of oleylalcohol, so that butoxyethyl oleate (158 g) was obtained. This compoundwas measured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Comparative 1

Comparative 1 was performed in the same manner as in Example 1 exceptthat 2-ethylhexanol (71 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that2-ethylhexyl oleate (161 g) was obtained. The obtained compound wasmeasured in terms of the physical properties thereof (i.e., thermalconductivity, kinematic viscosity, viscosity index, density and volumeresistivity).

Comparative 2

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co.,Ltd.) was measured in terms of the physical properties thereof (i.e.,thermal conductivity, kinematic viscosity, viscosity index, density andvolume resistivity).

Physical Properties Measuring Method (1) Thermal Conductivity

A thermal conductivity was measured using a single needle sensor ofKD2pro thermal properties analyzer manufactured by Decagon Device, Inc.at a room temperature of 25 degrees C.

(2) Volume Resistivity

A volume resistivity was measured at a room temperature of 25 degrees C.in accordance with JIS (Japanese Industrial Standards) C2101, 24 (VolumeResistivity Test).

(3) Kinematic Viscosity

A kinematic viscosity was measured according to “Test Methods forKinematic Viscosity of Petroleum Products” defined in JIS K 2283.

(4) Viscosity Index

A viscosity index was measured according to “Test Methods for KinematicViscosity of Petroleum Products” defined in JIS K 2283.

(5) Density

A density was measured in accordance with JIS K2249, “Crude Oil andPetroleum Product—Density Test Method”.

(6) Total Number of Terminal Methyl Group, Methylene Group and EtherGroup in Main Chain and Total Number of Methyl Branch and Ethyl Branchin Molecule

After formation of a target product was confirmed by 6850 GasChromatograph (manufactured by Agilent Technologies) and AL-400 NMR(manufactured by JEOL Ltd.), the total number of a terminal methylgroup, a methylene group and an ether group in a main chain and thetotal number of a methyl branch and an ethyl branch in a molecule wereobtained according to a structural formula of the target product.

Evaluation Result

As understood from the results of Table 1, the base oil (a compound)according to this exemplary embodiment in each of Examples 1 to 7 was apredetermined ester or ether. Since the ester and the ether each had 23or more of the total number of the terminal methyl group, the methylenegroup and the ether group in the main chain and 1 or less of the totalnumber of the methyl branch and the ethyl branch in a molecule, theester and the ether exhibited excellent thermal conductivity (coolingproperties) and electrical insulation properties. Further, these baseoils were excellent in lubricating properties because the kinematicviscosities thereof were within the predetermined range. Thus, it isunderstandable that a device-cooling oil using the base oil according tothe invention is favorably usable as a dual-purpose oil not only forcooling a motor, a battery, an inverter, an engine, an electric cell orthe like in an electric vehicle or a hybrid vehicle but also forlubricating a transmission or the like.

On the other hand, although the base oil in Comparative 1 was an esterobtained from alcohol having 8 carbon atoms in the same manner as inExample 3, the total number of a terminal methyl group, a methylenegroup and an ether group in a main chain was small, so that the base oilexhibited a poor thermal conductivity. In Comparative 2 in which thepurified mineral oil was used, since the base oil was a mixture of manykinds of isomers, the above parameters on the main chain and themolecule were not within a predetermined range, so that the base oilexhibited a poor thermal conductivity.

Second Exemplary Embodiment

The base oil according to the first exemplary embodiment contains atleast one of the oleyl ester (oleate, oleyl alcohol ester) and the oleylether as a fundamental component.

A device-cooling base oil according to a second exemplary embodiment ofthe invention contains at least one of an aliphatic monoester and analiphatic monoether as a basic component.

The total number of a terminal methyl group, a methylene group and anether group in a main chain of the monoester and the monoether is 18 ormore. The total number of a methyl branch and an ethyl branch in amolecule of the monoester and the monoether is 2 or less. The “mainchain” herein means a portion having the longest chain structure in themolecule.

The second exemplary embodiment will be described in detail below.

In describing this exemplary embodiment, what has been described in theabove first exemplary embodiment will be omitted or simplified.

In this exemplary embodiment, the aliphatic monoester and the aliphaticmonoether are used as main components of the base oil. The total numberof the terminal methyl group, the methylene group and the ether group inthe main chain in each of the ester and the ether is 18 or more in termsof an enhancement of cooling properties. Moreover, the total number ofthe methyl branches and the ethyl branches in a molecule of the esterand the ether is 2 or less in terms of an enhancement of coolingproperties. The number of the methylene group in each of the ester andthe ether is preferably 17 or more in terms of an enhancement of coolingproperties. _(>)In terms of the cooling properties, the ester and theether each preferably have a chain structure, more preferably a linearchain structure including no branch.

Such an ester is obtainable by typically known methods of manufacturingesters. A method of manufacturing the oleyl ester is subject to nolimitation. For instance, the ester is obtainable by adehydro-condensation reaction between a carboxylic acid and alcohol, acondensation reaction between a carboxylic halide or alcohol, and atransesterification. For instance, a starting material having a longlinear alkyl chain is preferably used for synthetic reaction such thatthe total number of the terminal methyl group, the methylene group andthe ether group in the main chain (i.e., the longest chain in amolecule) is 18 or more and the total number of a short alkyl side chainin the molecule (i.e., the methyl branch and the ethyl branch) is 2 orless.

Examples of the carboxylic acid (the starting material) includemonocarboxylic acids such as oleic acid, n-hexanoic acid, n-heptanoicacid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoicacid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid,ethylhexanoate, butyl octanoic acid, pentyl nonanoic acid, hexyldecanoic acid, heptyl undecanoic acid, octyldodecanoic acid, methylheptadecanoic acid and benzoic acid. As a starting material formanufacturing esters, a carboxylic acid ester and a carboxylic acidchloride, which are derivatives of the above carboxylic acids, areusable.

Examples of the alcohol (the starting material) include a monool such asn-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol,n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol,butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol,octyldodecanol, methylheptadecanol, benzyl alcohol, ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonopropyl ether, ethylene glycol monobutyl ether, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycolmonopropyl ether, diethylene glycol monobutyl ether, triethylene glycolmonomethyl ether, triethylene glycol monoethyl ether, triethylene glycolmonopropyl ether and triethylene glycol monobutyl ether.

A catalyst such as titanium tetraisopropoxide may be used as anesterification catalyst, or no catalyst may be used.

The ether may be manufactured by a typical ether manufacturing methodsuch as the Williamson ether synthetic method, but the manufacturingmethod of the ether is subject to no limitation.

The base oil of the exemplary embodiment contains 30 mass % or more ofthe ester and the ether, preferably 50 mass % or more, more preferably60 mass % or more, further preferably 70 mass % or more, particularlypreferably 80 mass % or more. When the base oil contains the ester andthe ether at less than 30 mass %, the base oil may not exhibit asufficient cooling properties. It should be noted that a base oil forcooling a device may be provided only by the base oil of the exemplaryembodiment (at 100 mass %).

The base oil of the exemplary embodiment has a kinematic viscosity at 40degrees C. in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to20 mm²/s, in the same manner as in the above-mentioned exemplaryembodiment. If the kinematic viscosity of the base oil at 40 degrees C.is less than 4 mm²/s, for instance, when the base oil is used as adual-purpose oil not only for a motor but also for a transmission or thelike, the base oil may exhibit an insufficient lubricity. On the otherhand, if the kinematic viscosity of the base oil at 40 degrees C.exceeds 30 mm²/s, the cooling properties may be insufficient.Additionally, when such a base oil is used as a cooling oil for a motoror the like, the cooling oil is unlikely to smoothly circulate within asystem or the like.

According to the exemplary embodiment, the thermal conductivity of thebase oil at 25 degrees C. is preferably 0.142 W/(m·K) or more, morepreferably 0.144 W/(m·K) or more in terms of the cooling properties, inthe same manner as in the above-mentioned exemplary embodiment.

The base oil of the exemplary embodiment preferably has a volumeresistivity at 25 degrees C. of 10¹⁰ Ω·cm or more, more preferably 10¹¹Ω·cm or more, further preferably 10¹² Ω·cm or more, particularlypreferably 10¹³ Ω·cm or more.

The base oil of the exemplary embodiment may be provided by blending theabove-mentioned ester and ether with an additional component (base oil)that is the same as one described in the first exemplary embodiment.

The device-cooling oil containing the base oil of the exemplaryembodiment is favorably usable for cooling a motor, a battery, aninverter, an engine and an electric cell or the like in an electricvehicle, a hybrid vehicle or the like, in the same manner as in theabove-mentioned exemplary embodiment. Since the viscosity of the baseoil at 40 degrees C. is in the above predetermined range, thedevice-cooling oil is excellent in lubricity, and thus is favorablyusable as a dual-purpose oil not only for cooling but also forlubricating a planetary gear, a transmission or the like.

The same additives as ones described in the first exemplary embodimentmay be blended in the device-cooling oil of the exemplary embodiment aslong as an object of the invention is attainable.

Examples of Second Exemplary Embodiment

Next, the second exemplary embodiment will be further described indetail based on Examples, which by no means limit the first exemplaryembodiment.

Specifically, base oils shown in Table 2 were prepared and variousevaluations thereof were conducted. Preparation methods of the base oilsare described below.

Evaluation was conducted by the same method as the property measurementmethod in Examples of the first exemplary embodiment.

TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Base Oil(Compound Name) 16- 2- 16- n-decanoic n-octanoic methylheptadecanoicheptylundecanoic methylheptadecanoic acid n-decyl acid 2- acid n-dodecylacid n-dodecyl acid 16- octyldodecyl methylheptadecyl- Total of terminalmethyl, 28 22 32 20 19 methylene and ether in main chain Total of methyland ethyl 1 0 2 0 0 branches in molecule Thermal Conductivity (25° C.)0.148 0.145 0.145 0.142 0.142 W/m · K Volume Resistivity (25° C.)1.1E+13 1.6E+13 1.7E+13 9.0E+12 1.3E+13 Ω · cm Kinematic Viscosity (40°C.) 15.90 12.71 22.97 5.487 10.49 mm²/s Kinematic Viscosity (100° C.)4.146 3.367 5.080 1.980 2.973 mm²/s Viscosity Index 176 144 157 — 145Density (15° C.) g/cm³ 0.8663 0.8560 0.8644 0.8610 0.8587 Example 6Example 7 Comp. 1 Comp. 2 Comp. 3 Comp. 4 Base Oil (Compound Name) 2-triethylene glycol 3,5,5- 2,2,4,8,10,10,- 1-decanol group-IIoctyldodecyl monobutyl ether n- trimethyl- hexamethyl-5- purifiedn-octyl ether octanoic acid ester hexanoic undecanoic acid mineral oilacid 2- 3,5,5-trimethyl octyldodecyl hexyl Total of terminal methyl, 2021 15 9 10 mixture methylene and ether in main chain Total of methyl andethyl 0 0 3 9 0 mixture of branches in molecule plural kinds ThermalConductivity (25° C.) 0.144 0.144 0.132 0.107 0.153 0.130 W/m · K VolumeResistivity (25° C.) 8.7E+13 5.6E+10 4.2E+13 1.1E+14 2.8E+09 1.2E+15 Ω ·cm Kinematic Viscosity (40° C.) 9.844 5.166 13.19 23.55 8.371 9.898mm²/s Kinematic Viscosity (100° C.) 2.830 1.859 3.389 3.977 1.838 2.722mm²/s Viscosity Index 141 — 135 27 — 116 Density (15° C.) g/cm³ 0.82750.9527 0.8570 0.8578 0.8340 0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus,16-methylheptadecanoic acid (128 g, product name: Isostearic acid EX,manufactured by KOKYU ALCOHOL KOGYO CO., LTD), 1-dodecyl alcohol (101 g,a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixedxylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co.,Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured byTokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at140 degrees C. for two hours while water was distilled away undernitrogen stream with stirring. Subsequently, the reaction product waswashed with saturated saline three times and with 0.1 N aqueous sodiumhydroxide three times and was then dried with anhydrous magnesiumsulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.).After filtration of magnesium sulfate, excessive alcohol (the startingmaterial) was distilled away to obtain 16-methylheptadecanoic acidn-dodecyl (182 g). This compound was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density). The results are shownin Table 2. The results of the following Examples and Comparatives arealso shown in Table 2.

Example 2

Example 2 was performed in the same manner as in Example 1 except that2-heptyl undecanoic acid (128 g, a reagent manufactured by TokyoChemical Industry Co., Ltd.) was used in place of 16-methylheptadecanoicacid (128 g), so that 2-heptylundecanoic acid n-dodecyl (180 g) wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Example 3

Example 3 was performed in the same manner as in Example 1 except that16-methylheptadecaol (134 g, product name: Isostearyl Alcohol EX, KOKYUALCOHOL KOGYO CO., LTD) was used in place of 1-dodecyl alcohol (101 g),so that 16-methylheptadecanoic acid 16-methylheptadecyl (206 g) wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except thatn-decanoic acid (78 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.) and 1-decyl alcohol (86 g, a reagent manufactured by TokyoChemical Industry Co., Ltd.) were used in place of 128 g of16-methylheptadecanoic acid and 101 g of 1-dodecyl alcohol, so thatn-decanoic acid n-dodecyl (132 g) was obtained. This compound wasmeasured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Example 5

Example 5 was performed in the same manner as in Example 1 except thatn-octanoic acid (72 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.) and 2-octyldodecanol (119 g, product name: NJCOL 200A,manufactured by New Japan chemical Co., Ltd.) were used in place of 128g of 16-methylheptadecanoic acid and 1-dodecyl alcohol (101 g), so thatn-octanoic acid 2-octyldodecyl (132 g) was obtained. This compound wasmeasured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Example 6

To a 2-L glass flask, 2-octyldodecanol (300 g, product name: NJCOL 200A,manufactured by New Japan chemical Co., Ltd.), 1-bromooctane (300 g, areagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutylammonium bromide (30 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.), and an aqueous sodium hydroxide (500 g, obtained bydissolving 150 g of sodium hydroxide in 350 g of water). The mixture wasreacted at 50 degrees C. for 20 hours with stirring. After the reaction,the reaction mixture was transferred to a separating funnel. An organicphase was washed five times with water (500 mL). Subsequently, theorganic phase was distilled, so that 2-octyldodecyl n-octyl ether (266g) was obtained. This compound was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density).

Example 7

Example 7 was performed in the same manner as in Example 1 except thatn-octanoic acid (144 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and triethylene glycol monobutyl ether (165 g, areagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used inplace of 128 g of 16-methylheptadecanoic acid and 101 g of 1-dodecylalcohol, so that 188 g of n-octanoic acid ester of triethylene glycolmonobutyl ether was obtained. This compound was measured in terms of thephysical properties thereof (i.e., thermal conductivity, volumeresistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Comparative 1 was performed in the same manner as in Example 1 exceptthat 3,5,5-trimethylhexanoic acid (79 g, a reagent manufactured by TokyoChemical Industry Co., Ltd.) and 2-octyldodecanol (119 g, product name:NJCOL 200A, manufactured by New Japan chemical Co., Ltd.) were used inplace of 16-methylheptadecanoic acid (128 g) and 1-dodecyl alcohol (101g), so that 139 g of 3,5,5-trimethylhexanoic acid 2-octyldodecyl wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Comparative 2

Comparative 2 was performed in the same manner as in Example 1 exceptthat 2,2,4,8,10,10-hexamethyl-5-undecanoic acid (114 g, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) and 3,5,5-trimethylhexanol (72 g, a reagent manufactured by Tokyo Chemical Industry Co.,Ltd.) were used in place of 16-methylheptadecanoic acid (128 g) and1-dodecyl alcohol (101 g), so that 148 g of2,2,4,8,10,10-hexamethyl-5-undecanoic acid 3,5,5-trimethyl hexyl wasobtained. This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Comparative 3

1-decanol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.)was measured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Comparative 4

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co.,Ltd.) was measured in terms of the physical properties thereof (i.e.,thermal conductivity, volume resistivity, kinematic viscosity, viscosityindex, and density).

Evaluation Result

As is obvious from the results shown in Table 2, in each of the baseoils (compounds) of Examples 1 to 7 according to the exemplaryembodiment, the total number of a terminal methyl group(s), a methylenegroup(s) and an ether group(s) in the main chain was 18 or more and thetotal number of a methyl branch and an ethyl branch in a molecule was 2or less, so that these base oils were excellent in thermal conductivity(cooling properties) and electrical insulation properties. Further,these base oils were excellent in lubricating properties because thekinematic viscosities thereof were within the predetermined range. Thus,it is understandable that a device-cooling oil using the base oilaccording to the invention is favorably usable as a dual-purpose oil notonly for cooling a motor, a battery, an inverter, an engine, an electriccell or the like in an electric vehicle or a hybrid vehicle but also forlubricating a transmission or the like.

On the other hand, although the base oil of Comparative 1 is an esterobtained from 2-octyldodecanol in the same manner as in Example 5, thebase oil exhibits a poor thermal conductivity because of a large numberof methyl branches. The ester of Comparative 2 exhibits an extremelypoor thermal conductivity because of an extremely large number of methylbranches. The base oil of Comparative 3 is alcohol and exhibits afavorable thermal conductivity but exhibits poor electrical insulationproperties. In Comparative 4 in which the purified mineral oil was used,since the base oil was a mixture of many kinds of isomers, the aboveparameters on the main chain and the molecule were not within apredetermined range, so that the base oil exhibited a poor thermalconductivity.

Third Exemplary Embodiment

The base oil according to the first exemplary embodiment contains atleast one of the oleyl ester (oleate, oleyl alcohol ester) and the oleylether as a fundamental component. The base oil according to the secondexemplary embodiment contains at least one of the aliphatic monoesterand the aliphatic monoether as a fundamental component.

The device-cooling base oil according to the third exemplary embodimentof the invention contains at least one of a divalent aliphaticcarboxylic acid diester and a divalent aliphatic alcohol diether as afundamental component.

The aliphatic diester and the aliphatic diether each have 20 or more ofa total number of a terminal methyl group, a methylene group and anether group in a main chain and 2 or less of a total number of a methylbranch and an ethyl branch in the aliphatic diester and the aliphaticdiether. The “main chain” herein means a portion having the longestchain structure in the molecule.

The third exemplary embodiment will be described in detail below.

In describing this exemplary embodiment, what has been described in theabove first and second exemplary embodiments will be omitted orsimplified.

In this exemplary embodiment, at least one of the aliphatic diester andthe aliphatic diether is used as main components of the base oil. Thealiphatic diester and the aliphatic diether each have 20 or more of thetotal number of the terminal methyl group, the methylene group and theether group in the main chain and 2 or less of the total number of themethyl branch and the ethyl branch in the molecule. The number of themethylene group in the diester and the diether is preferably 18 or more,more preferably 19 or more in terms of an enhancement of coolingproperties.

The diester and the diether preferably have a linear chain structure interms of an enhancement of the cooling properties of the base oil.

Such an aliphatic diester is obtainable by typically known methods ofmanufacturing esters. A method of manufacturing the aliphatic diesterester is subject to no limitation. For instance, the aliphatic diesteris obtainable by: a dehydration condensation reaction between a divalentcarboxylic acid and alcohol or a dehydration condensation reactionbetween divalent alcohol and a carboxylic acid; a condensation reactionbetween a divalent carboxylic acid dihalide and alcohol or acondensation reaction between divalent alcohol and a carboxylic acidhalide; and a transesterification. For instance, a starting materialhaving a long linear alkyl chain is preferably used for syntheticreaction such that the total number of the terminal methyl group, themethylene group and the ether group in the main chain (i.e., the longestchain in a molecule) is 20 or more and the total number of a short alkylside chain in the molecule (i.e., the methyl branch and the ethylbranch) is 2 or less.

Examples of the carboxylic acid (the starting material) include:dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and1,10-decamethylene dicarboxylic acid; monocarboxylic acids such asn-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid,n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid,n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid,ethylhexanoate, and butyl octanoic acid. As a starting material formanufacturing esters, a carboxylic acid ester and a carboxylic acidchloride, which are derivatives of the above carboxylic acids, areusable.

Examples of the alcohol (the starting material) include: a monool suchas n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol,n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol,butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol,octyldodecanol, and methylheptadecanol; and a diol such as ethyleneglycol, 1,3-propane diol, 1,4-butanediol, 1,5-pentanediol,1,6-hexandiol, diethylene glycol, triethylene glycol, tetraethyleneglycol, polyethylene glycol and polytetramethylene glycol.

A catalyst such as titanium tetraisopropoxide may be used as anesterification catalyst, or no catalyst may be used.

The diether may be manufactured by a typical ether manufacturing methodsuch as the Williamson ether synthetic method, but the manufacturingmethod of the ether is subject to no limitation.

The base oil of the exemplary embodiment contains 30 mass % or more ofthe diester and the diether, preferably 50 mass % or more, morepreferably 60 mass % or more, further preferably 70 mass % or more,particularly preferably 80 mass % or more. When the base oil containsthe diester and the diether at less than 30 mass %, the base oil may notexhibit a sufficient cooling properties. It should be noted that a baseoil for cooling a device may be provided only by the base oil of theexemplary embodiment (at 100 mass %).

The base oil of the exemplary embodiment has a kinematic viscosity at 40degrees C. in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to20 mm²/s, in the same manner as in the above-mentioned exemplaryembodiment. If the kinematic viscosity of the base oil at 40 degrees C.is less than 4 mm²/s, for instance, when the base oil is used as adual-purpose oil not only for a motor but also for a transmission or thelike, the base oil may exhibit an insufficient lubricity. On the otherhand, if the kinematic viscosity of the base oil at 40 degrees C.exceeds 30 mm²/s, the cooling properties may be insufficient.Additionally, when such a base oil is used as a cooling oil for a motoror the like, the cooling oil is unlikely to smoothly circulate within asystem or the like.

According to the exemplary embodiment, the thermal conductivity of thebase oil at 25 degrees C. is preferably 0.142 W/(m·K) or more, morepreferably 0.144 W/(m·K) or more in terms of the cooling properties, inthe same manner as in the above-mentioned exemplary embodiment.

In terms of electrical insulation properties, the base oil of theexemplary embodiment preferably has a volume resistivity at 25 degreesC. of 10¹⁰ Ω·cm or more, more preferably 10¹¹ Ω·cm or more, furtherpreferably 10¹² Ω·cm or more.

The base oil of the exemplary embodiment may be provided by blending theabove-mentioned ester and ether with an additional component (base oil)that is the same as one described in the first exemplary embodiment.

The device-cooling oil containing the base oil of the exemplaryembodiment is favorably usable for cooling a motor, a battery, aninverter, an engine and an electric cell or the like in an electricvehicle, a hybrid vehicle or the like, in the same manner as in theabove-mentioned exemplary embodiment. Since the viscosity of the baseoil at 40 degrees C. is in the above predetermined range, thedevice-cooling oil is excellent in lubricity, and thus is favorablyusable as a dual-purpose oil not only for cooling but also forlubricating a planetary gear, a transmission or the like.

The same additives as ones described in the first exemplary embodimentmay be blended in the device-cooling oil of the exemplary embodiment aslong as an object of the invention is attainable.

Examples of Third Exemplary Embodiment

Next, the third exemplary embodiment will be further described in detailbased on Examples, which by no means limit the first exemplaryembodiment.

Specifically, base oils shown in Table 3 were prepared and variousevaluations thereof were conducted. Preparation methods of the base oilsare described below.

Evaluation was conducted by the same method as the property measurementmethod in Examples of the first exemplary embodiment.

TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 BaseOil (Compound Name) azelaic azelaic dodecanedioic sebacic acidbis-n-octyl 2-ethyl- acid acid acid di-2- n-octyl 2- 1,4-butane hexanoicacid di-n-octyl n-octyl 2- ethylhexyl ethylhexyl diether diester ofpoly- ethylhexyl tetrahydrofuran 250 Total of terminal methyl, 25 22.222 23.3 22 27 methylene and ether in main (average) (average) (average)chain Total of methyl and ethyl 0 0.95 2 0.9 0 2 branches in molecule(average) (average) Thermal Conductivity (25° C.) 0.148 0.144 0.1430.145 0.142 0.146 W/m · K Volume Resistivity (25° C.) 1.6E+11 3.5E+111.7E+12 8.7E+11 2.6E+12 1.0E+11 Ω · cm Kinematic Viscosity (40° C.)11.02 10.75 14.09 11.67 4.809 22.45 mm²/s Kinematic Viscosity (100° C.)3.300 3.139 3.764 3.353 1.788 4.989 mm2/s Viscosity Index 188 168 168174 — 156 Density (15° C.) g/cm³ 0.9167 0.9184 0.9130 0.9156 0.85050.9515 Example 7 Comp. 1 Comp. 2 Comp. 3 Comp. 4 Base Oil (CompoundName) triethylene glycol azelaic acid di- neopentyl glycol neopentylgroup-II n-octanoic acid 2-ethylhexyl n-octanoic acid glycol 2- purifieddiester diester ehtylhexane mineral oil acid diester Total of terminalmethyl, 24 19 18 12 mixture methylene and ether in main chain Total ofmethyl and ethyl 0 2 2 4 mixture of branches in molecule plural kindsThermal Conductivity (25° C.) 0.147 0.137 0.133 0.123 0.130 W/m · KVolume Resistivity (25° C.) 1.9E+10 5.9E+11 3.4E+11 2.9E+12 1.2E+15 Ω ·cm Kinematic Viscosity (40° C.) 8.918 10.48 7.161 7.486 9.898 mm²/sKinematic Viscosity (100° C.) 2.720 2.991 2.257 2.076 2.722 mm2/sViscosity Index 158 149 133 58 116 Density (15° C.) g/cm³ 0.9740 0.92060.9230 0.9185 0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus,azelaic acid (94 g, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.), 1-octanol (156 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured byTokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) wereput. A reaction was conducted at 140 degrees C. for two hours whilewater was distilled away under nitrogen stream with stirring.Subsequently, the reaction product was washed with saturated salinethree times and with 0.1 N aqueous sodium hydroxide three times and wasthen dried with anhydrous magnesium sulfate (a reagent manufactured byTokyo Chemical Industry Co., Ltd.). After filtration of magnesiumsulfate, excessive alcohol (the starting material) was distilled away toobtain azelaic acid di-n-octyl (188 g). This compound was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).The results are shown in Table 3. The results of the following Examplesand Comparatives are also shown in Table 3.

Example 2

Example 2 was performed in the same manner as in Example 1 except that75 g of azelaic acid, 53 g of 1-octanol (a reagent manufactured by TokyoChemical Industry Co., Ltd.) and 65 g of 2-ethylhexanol (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of94 g of azelaic acid and 156 g of 1-octanol, so that 145 g of a mixturecontaining 30 mass % of azelaic acid di-n-octyl, 45 mass % of azelaicacid n-octyl 2-ethylhexyl, and 25 mass % of azelaic acid di-2-ethylhexylwas obtained. This compound was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density).

Example 3

Dodecanedioic acid di-2-ethylhexyl (a reagent manufactured by TokyoChemical Industry Co., Ltd.) was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that81 g of sebacic acid, 53 g of 1-octanol (a reagent manufactured by TokyoChemical Industry Co., Ltd.) and 65 g of 2-ethylhexanol (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of94 g of azelaic acid and 156 g of 1-octanol, so that 147 g of a mixturecontaining 32 mass % of sebacic acid di-n-octyl, 46 mass % of sebacicacid n-octyl 2-ethylhexyl, and 22 mass % of sebacic acid di-2-ethylhexylwas obtained. This compound was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density).

Example 5

To a 1-L glass flask, 1,4-butanediol (27 g, a reagent manufactured byTokyo Chemical Industry Co., Ltd.), 1-bromooctane (174 g, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammoniumbromide (10 g, a reagent manufactured by Tokyo Chemical Industry Co.,Ltd.), and an aqueous sodium hydroxide (200 g, obtained by dissolving 60g of sodium hydroxide in 140 g of water). A mixture was reacted at 70degrees C. for 20 hours with stirring. After the reaction, the reactionmixture was transferred to a separating funnel. An organic phase waswashed five times with water (300 mL). Subsequently, excessive1-bromooctane was distilled, so that bis-n-octyl 1,4-butane diether (76g) was obtained. This compound was measured in terms of the physicalproperties thereof (i.e., thermal conductivity, volume resistivity,kinematic viscosity, viscosity index and density).

Example 6

Example 6 was performed in the same manner as in Example 1 except that2-ethyl hexanoic acid (130 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and polytetrahydrofuran 250 (75 g, a reagentmanufactured by Sigma-Aldrich Co. LLC.) were used in place of 94 g ofazelaic acid and 156 g of 1-octanol, so that 126 g of 2-ethylhexanoicacid diester of polytetrahydrofuran 250 was obtained. This ester wasmeasured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Example 7

Example 7 was performed in the same manner as in Example 1 except thatn-octanoic acid (180 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and triethylene glycol (75 g, a reagent manufacturedby Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g ofazelaic acid and 156 g of 1-octanol, so that 163 g of n-octanoic aciddiester of triethylene glycol was obtained. This ester was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Azelaic acid di-2-ethylhexyl (a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Comparative 2

Comparative 2 was performed in the same manner as in Example 1 exceptthat n-octanoic acid (173 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and neopentyl glycol (52 g, a reagent manufacturedby Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g ofazelaic acid and 156 g of 1-octanol, so that 160 g of neopentyl glycoln-octanoic acid diester was obtained. This compound was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 3

Comparative 3 was performed in the same manner as in Example 1 exceptthat 2-ethylhexane acid (165 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and neopentyl glycol (52 g, a reagent manufacturedby Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g ofazelaic acid and 156 g of 1-octanol, so that 160 g of neopentyl glycol2-ethylhexane acid diester was obtained. This compound was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 4

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co.,Ltd.) was measured in terms of the physical properties thereof (i.e.,thermal conductivity, volume resistivity, kinematic viscosity, viscosityindex, and density).

Evaluation Result

As understood from the results of Table 3, the base oil (a compound)according to this exemplary embodiment in each of Examples 1 to 7 was apredetermined ester or ether. Since the ester and the ether each had 20or more of the total number of the terminal methyl group, the methylenegroup and the ether group in the main chain and 2 or less of the totalnumber of the methyl branch and the ethyl branch in a molecule, theester and the ether exhibited excellent thermal conductivity (coolingproperties) and electrical insulation properties. Further, these baseoils were excellent in lubricating properties because the kinematicviscosities thereof were within the predetermined range. Thus, it isunderstandable that a device-cooling oil using the base oil according tothe exemplary embodiment is favorably usable as a dual-purpose oil notonly for cooling a motor, a battery, an inverter, an engine, an electriccell or the like in an electric vehicle or a hybrid vehicle but also forlubricating a transmission or the like.

On the other hand, the esters of Comparatives 1 and 2 had a poor thermalconductivity because of the short main chain and a small number of themethylene groups. The ester of Comparative 3 had an extremely poorthermal conductivity because of a large number of the methyl branchesand the ethyl branches in addition to the short main chain and the smallnumber of the methylene groups. In Comparative 4 in which the purifiedmineral oil was used, since the base oil was a mixture of many kinds ofisomers, the above parameters on the main chain and the molecule werenot within a predetermined range, so that the base oil exhibited a poorthermal conductivity.

Fourth Exemplary Embodiment

The base oil according to the first exemplary embodiment contains atleast one of the oleyl ester (oleate, oleyl alcohol ester) and the oleylether as a fundamental component. The base oil according to the secondexemplary embodiment contains at least one of the aliphatic monoesterand the aliphatic monoether as a fundamental component. The base oilaccording to the third exemplary embodiment contains at least one of thedivalent aliphatic carboxylic acid diester, the divalent aliphaticalcohol diester and the divalent aliphatic alcohol diether as a basiccomponent.

The device-cooling base oil according to a fourth exemplary embodimentof the invention contains at least one of aliphatic triester, aliphatictriether, aliphatic tri(etherester), aliphatic tetraester, aliphatictetraether, aliphatic tetra(etherester), aromatic diester, aromaticdiether and aromatic di(etherester) as a main component of the base oil.

Each of molecules of the esters, the ethers and the etheresters have 18or more of a total number of a terminal methyl group, a methylene groupand an ether group in a main chain. Each of the molecules of the estersand the ethers has 1 or less of a total number of a methyl branch and anethyl branch. Herein, the main chain refers to the longest chain, whichmay interpose an aromatic ring, in a molecule. The aliphatictri(etherester) refers to a compound having three in total of an ethergroup and an ester group. The aliphatic tetra(etherester) refers to acompound having four in total of an ether group and an ester group.Aromatic di(etherester) refers to a compound having two in total of anether group and an ester group.

The fourth exemplary embodiment will be described in detail below.

In describing this exemplary embodiment, what has been described in theabove first to third exemplary embodiments will be omitted orsimplified.

As described in the first exemplary embodiment, in order to improvethermal conductivity in liquid molecules and increase collisionfrequency between the molecules, the ester and the ether having a longchain structure are advantageous. Since the aromatic ring is so rigid asto hardly diffuse molecular vibrational energy, even when long chainstructures are bonded to each other through the aromatic ring, a thermalconductivity is hardly reduced. Accordingly, when an aromatic compoundis used in the exemplary embodiment, the longest chain interposing thearomatic ring is defined as the main chain.

In the exemplary embodiment, at least one of aliphatic triester,aliphatic triether, aliphatic tri(etherester), aliphatic tetraester,aliphatic tetraether, aliphatic tetra(etherester), aromatic diester,aromatic diether and aromatic di(etherester) is used as a main componentof the base oil. The total number of the terminal methyl group, themethylene group and the ether group in the main chain in each of theester, the ether and the etherester is 18 or more in terms of anenhancement of cooling properties. Moreover, the total number of themethyl branches and the ethyl branches in a molecule of the ester, theether and the etherester is 1 or less in terms of an enhancement ofcooling properties. The ester, the ether and the etherester preferablycontain none of the above-mentioned methyl branch and ethyl branch interms of an enhancement of cooling properties.

Such an ester is obtainable by typically known methods of manufacturingesters. A method of manufacturing the oleyl ester is subject to nolimitation. For instance, the ester is obtainable by adehydro-condensation reaction between a carboxylic acid and alcohol, acondensation reaction between a carboxylic halide or alcohol, and atransesterification. For instance, a starting material having a longlinear alkyl chain may be used for synthetic reaction such that thetotal number of the terminal methyl group, the methylene group and theether group in the main chain (i.e., the longest chain in a molecule) is18 or more and the total number of a short alkyl side chain in themolecule (i.e., the methyl branch and the ethyl branch) is 1 or less.

Examples of the carboxylic acid (the starting material) include analiphatic carboxylic acid and an aromatic carboxylic acid. Examples ofthe carboxylic acid include: monocarboxylic acids such n-hexanoic acid,n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid,n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid,n-tetradecanoic acid, oleic acid, ethylhexanoic acid, butyl octanoicacid, pentyl nonanoic acid, hexyl decanoic acid, heptyl undecanoic acid,octyldodecanoic acid, methyl heptadecanoic acid, salicylic acid,4-hydroxybenzoic acid, benzoic acid and phenylacetic acid; anddicarboxylic acids such as phthalic acid, isophthalic acid andterephthalic acid. As a starting material for manufacturing esters, acarboxylic acid ester and a carboxylic acid chloride, which arederivatives of the above carboxylic acids, are usable.

Examples of the alcohol (the starting material) include: a monool suchas n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol,n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol,butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol,octyldodecanol, methylheptadecanol, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monopropyl ether,ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monopropyl ether,diethylene glycol monobutyl ether, triethylene glycol monomethyl ether,triethylene glycol monoethyl ether, triethylene glycol monopropyl etherand triethylene glycol monobutyl ether; a triol such astrimethylolpropane and trimethylolethane; and a tetraol such aspentaerythritol.

A catalyst such as titanium tetraisopropoxide may be used as anesterification catalyst, or no catalyst may be used.

The ether may be manufactured by a typical ether manufacturing methodsuch as the Williamson ether synthetic method, but the manufacturingmethod of the ether is subject to no limitation.

The base oil of the exemplary embodiment contains 30 mass % or more ofthe ester and the ether, preferably 50 mass % or more, more preferably60 mass % or more, further preferably 70 mass % or more, particularlypreferably 80 mass % or more. When the base oil contains the ester andthe ether at less than 30 mass %, the base oil may not exhibit asufficient cooling properties. It should be noted that a base oil forcooling a device may be provided only by the base oil of the exemplaryembodiment (at 100 mass %).

The base oil of the exemplary embodiment has a kinematic viscosity at 40degrees C. in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to20 mm²/s, in the same manner as in the above-mentioned exemplaryembodiment. If the kinematic viscosity of the base oil at 40 degrees C.is less than 4 mm²/s, for instance, when the base oil is used as adual-purpose oil not only for a motor but also for a transmission or thelike, the base oil may exhibit an insufficient lubricity. On the otherhand, if the kinematic viscosity of the base oil at 40 degrees C.exceeds 30 mm²/s, the cooling properties may be insufficient.Additionally, when such a base oil is used as a cooling oil for a motoror the like, the cooling oil is unlikely to smoothly circulate within asystem or the like.

According to the exemplary embodiment, the thermal conductivity of thebase oil at 25 degrees C. is preferably 0.142 W/(m·K) or more, morepreferably 0.144 W/(m·K) or more in terms of the cooling properties, inthe same manner as in the above-mentioned exemplary embodiment.

The base oil of the exemplary embodiment preferably has a volumeresistivity at 25 degrees C. of 10¹⁰ Ω·cm or more, more preferably10¹¹Ω·cm or more, further preferably 10¹² Ω·cm or more, particularlypreferably 10¹³ Ω·cm or more.

The base oil of the exemplary embodiment may be provided by blending theabove-mentioned ester and ether with an additional component (base oil)that is the same as one described in the first exemplary embodiment.

The device-cooling oil containing the base oil of the exemplaryembodiment is favorably usable for cooling a motor, a battery, aninverter, an engine and an electric cell or the like in an electricvehicle, a hybrid vehicle or the like, in the same manner as in theabove-mentioned exemplary embodiment. Since the viscosity of the baseoil at 40 degrees C. is in the above predetermined range, thedevice-cooling oil is excellent in lubricity, and thus is favorablyusable as a dual-purpose oil not only for cooling but also forlubricating a planetary gear, a transmission or the like.

The same additives as ones described in the first exemplary embodimentmay be blended in the device-cooling oil of the exemplary embodiment aslong as an object of the invention is attainable.

Examples of Fourth Exemplary Embodiment

Next, the fourth exemplary embodiment will be further described indetail based on Examples, which by no means limit the first exemplaryembodiment.

Specifically, base oils shown in Table 4 were prepared and variousevaluations thereof were conducted. Preparation methods of the base oilsare described below.

Evaluation was conducted by the same method as the property measurementmethod in Examples of the first exemplary embodiment.

TABLE 4 Example 1 Example 2 Example 3 Example 4 Example 5 Comp. 1 Comp.2 Comp. 3 Base Oil (Compound Name) penta- trimethylol- phthalic acidisophthalic mixture of n- trimethylol- phthalic acid group-II erythritolpropane di-n-dodecyl acid octanoic acid propane di-2-ethylhexyl purifiedtetra-n- tri-n- di-n-octyl ester/n-octyl 2-ethyl hexanoic mineral oiloctanoic octanoic ether of acid triester acid ester acid estertrimethlol- propane Total of terminal methyl, 18 18 26 18 18 12 12mixture methylene and ether in main chain Total of methyl and ethyl 0 10 0 1 4 2 mixture of branches in molecule plural kinds ThermalConductivity (25° C.) 0.148 0.143 0.148 0.144 0.142 0.132 0.131 0.130W/m · K Volume Resistivity (25° C.) 1.5E+13 1.9E+12 8.6E+11 2.3E+114.6E+12 1.1E+14 2.5E+11 1.2E+15 Ω · cm Kinematic Viscosity (40° C.)25.81 16.77 28.46 22.13 11.43 24.11 27.08 9.898 mm²/s KinematicViscosity (100° C.) 5.315 3.940 5.409 4.336 3.106 4.265 4.230 2.722mm2/s Viscosity Index 145 134 128 102 138 66 16 116 Density (15° C.)g/cm³ 0.9680 0.9519 0.9494 0.9820 0.8838 0.9484 0.9873 0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus,n-octanoic acid (173 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.), pentaerythritol (34 g, a reagent manufactured byTokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.), and titaniumtetraisopropoxide (0.1 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) were put. A reaction was conducted at 140 degrees C.for two hours while water was distilled away under nitrogen stream withstirring. Subsequently, the reaction product was washed with saturatedsaline three times and with 0.1 N aqueous sodium hydroxide three timesand was then dried with anhydrous magnesium sulfate (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.). After filtration ofmagnesium sulfate, excessive alcohol (the starting material) wasdistilled away to obtain pentaerythritol tetra-n-octanoic acid ester(148 g). This compound was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density). The results are shown in Table4. The results of the following Examples and Comparatives are also shownin Table 4.

Example 2

Example 2 was performed in the same manner as in Example 1 except that159 g of n-octanoic acid and 40 g of trimethylolpropane (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of173 g of n-octanoic acid and 34 g of pentaerythritol, so that 139 g oftrimethylolpropane tri-n-octanoic acid ester was obtained. This compoundwas measured in terms of the physical properties thereof (i.e., thermalconductivity, volume resistivity, kinematic viscosity, viscosity indexand density).

Example 3

Example 3 was performed in the same manner as in Example 1 except thatphthalic anhydride (44 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and 1-dodecanol (149 g, a reagent manufactured byTokyo Chemical Industry Co., Ltd.) were used in place of 173 g ofn-octanoic acid and 34 g of pentaerythritol, so that 137 g of phthalicacid di-n-dodecyl was obtained. This compound was measured in terms ofthe physical properties thereof (i.e., thermal conductivity, volumeresistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except thatisophthalic acid (50 g, a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) and 1-octanol (104 g, a reagent manufactured byTokyo Chemical Industry Co., Ltd.) were used in place of 173 g ofn-octanoic acid and 34 g of pentaerythritol, so that 107 g ofisophthalic acid di-n-octyl was obtained. This compound was measured interms of the physical properties thereof (i.e., thermal conductivity,volume resistivity, kinematic viscosity, viscosity index and density).

Example 5

To a 1-L glass flask, trimethylolpropane (34 g, a reagent manufacturedby Tokyo Chemical Industry Co., Ltd.), 1-bromooctane (217 g, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammoniumbromide (10 g, a reagent manufactured by Tokyo Chemical Industry Co.,Ltd.), and an aqueous sodium hydroxide (200 g, obtained by dissolving 60g of sodium hydroxide in 140 g of water). The mixture was reacted at 70degrees C. for 20 hours with stirring. After the reaction, the reactionmixture was transferred to a separating funnel. An organic phase waswashed five times with water (300 mL), and then, excessive 1-bromooctanewas distilled from the reaction mixture. To a four-necked flask (500 mL)provided with a Dean-Stark device, the reaction mixture, n-octanoic acid(50 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.),mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical IndustryCo., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reactionwas conducted at 140 degrees C. for two hours while water was distilledaway under nitrogen stream with stirring, thereby esterifying unreactedalcohol portion of trimethylolpropane. After washing with saturatedsaline, excessive n-octanoic acid was distilled away. The obtainedproduct was washed with 0.1 N aqueous sodium hydroxide three times andwas dried with anhydrous magnesium sulfate (a reagent manufactured byTokyo Chemical Industry Co., Ltd.). After filtration of magnesiumsulfate, the solvent was distilled away, so that 102 g of a mixture of24% of n-octyltriether of trimethylolpropane, 58% of n-octyldiethern-octanoic acid monoester of trimethylolpropane, and 18% ofn-octylmonoether n-octanoic acid diester of trimethylolpropane. Thiscompound was measured in terms of the physical properties thereof (i.e.,thermal conductivity, volume resistivity, kinematic viscosity, viscosityindex and density).

Comparative 1

Trimethylolpropane 2-ethyl hexanoic acid triester (a reagentmanufactured by Tokyo Chemical Industry Co., Ltd.) was measured in termsof the physical properties thereof (i.e., thermal conductivity, volumeresistivity, kinematic viscosity, viscosity index and density).

Comparative 2

Phthalic acid di-2-ethylhexyl (a reagent manufactured by Tokyo ChemicalIndustry Co., Ltd.) was measured in terms of the physical propertiesthereof (i.e., thermal conductivity, volume resistivity, kinematicviscosity, viscosity index and density).

Comparative 3

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co.,Ltd.) was measured in terms of the physical properties thereof (i.e.,thermal conductivity, volume resistivity, kinematic viscosity, viscosityindex, and density).

Evaluation Result

As is obvious from the results shown in Table 4, in each of the baseoils (compounds) of Examples 1 to 5 according to the exemplaryembodiment, the total number of a terminal methyl group(s) and amethylene group(s) in the main chain was 18 or more and the total numberof a methyl branch and an ethyl branch in the molecule was 1 or less, sothat these base oils were excellent in thermal conductivity (coolingproperties) and electrical insulation properties. Further, these baseoils were excellent in lubricating properties because the kinematicviscosities thereof were within the predetermined range. Thus, it isunderstandable that a device-cooling oil using the base oil according tothe invention is favorably usable as a dual-purpose oil not only forcooling a motor, a battery, an inverter, an engine, an electric cell orthe like in an electric vehicle or a hybrid vehicle but also forlubricating a transmission or the like.

On the other hand, although the base oil of Comparative 1 was a triesterof trimethylolpropane in the same manner as the base oil of Example 2,the base oil of Comparative 1 exhibited a poor thermal conductivitybecause of a short main chain and a large number of ethyl branches.Although the base oil of Comparative 2 was a phthalic acid ester in thesame manner as the base oil of Example 3, the base oil of Comparative 2exhibited a poor thermal conductivity because of a short main chain anda large number of ethyl branches. In Comparative 3 in which the purifiedmineral oil was used, since the base oil was a mixture of many kinds ofisomers, the above parameters on the main chain and the molecule werenot within a predetermined range, so that the base oil exhibited a poorthermal conductivity.

INDUSTRIAL APPLICABILITY

The invention is applicable to a base oil for cooling a device, adevice-cooling oil using the base oil, a device to be cooled by thedevice-cooling oil, and a device cooling method using the device-coolingoil.

1. A base oil, comprising 30 mass % or more of at least one of an oleylester and an oleyl ether, wherein: the oleyl ester and the oleyl ethereach have 23 or more of a total number of a terminal methyl group, amethylene group and an ether group in a main chain; the oleyl ester andthe oleyl ether each have 1 or less of a total number of a methyl branchand an ethyl branch; and the base oil has a kinematic viscosity in arange of 4 mm²/s to 30 mm²/s.
 2. The base oil of claim 1, comprising 50mass % or more of the at least one of the oleyl ester and the oleylether.
 3. A base oil, comprising 30 mass % or more of at least one of analiphatic monoester and an aliphatic monoether, wherein: the aliphaticmonoester and the aliphatic monoether each have 18 or more of a totalnumber of a terminal methyl group, a methylene group and an ether groupin a main chain; the aliphatic monoester and the aliphatic monoethereach have 2 or less of a total number of a methyl branch and an ethylbranch; and the base oil has a kinematic viscosity in a range of 4 mm²/sto 30 mm²/s.
 4. The base oil of claim 3, wherein at least one of thealiphatic monoester and the aliphatic monoether has a chain structure.5. A base oil, comprising 30 mass % or more of at least one of analiphatic diester and an aliphatic diether, wherein: the aliphaticdiester and the aliphatic diether each have 20 or more of a total numberof a terminal methyl group, a methylene group and an ether group in amain chain; the aliphatic diester and the aliphatic diether each have 2or less of a total number of a methyl branch and an ethyl branch; andthe base oil has a kinematic viscosity in a range of 4 mm²/s to 30mm²/s.
 6. A base oil, comprising 30 mass % or more of at least onecompound selected from the group consisting of an aliphatic triester, analiphatic triether, an aliphatic tri(etherester), an aliphatictetraester, an aliphatic tetraether, an aliphatic tetra(etherester), anaromatic diester, an aromatic diether and an aromatic di(etherester),wherein: each of the at least one compound has 18 or more of a totalnumber of a terminal methyl group, a methylene group and an ether groupin a main chain, and 1 or less of a total number of a methyl branch andan ethyl branch; and the base oil has a kinematic viscosity in a rangeof 4 mm²/s to 30 mm²/s.
 7. The base oil of claim 1, wherein a thermalconductivity of the base oil at 25 degrees C. is 0.142 W/(m·K) or more.8. The base oil of claim 1, wherein a volume resistivity of the base oilat 25 degrees C. is 10¹⁰ Ω·cm or more.
 9. A device-cooling oil,comprising the base oil of claim
 1. 10. A device configured to be cooledby the device-cooling oil of claim
 9. 11. The device of claim 10,wherein the device is suitable for an electric vehicle or a hybridvehicle.
 12. The device of claim 10, wherein the device is at least oneselected from the group consisting of a motor, a battery, an inverter,an engine and an electric cell.
 13. A device cooling method, comprisingcontacting a device with the device-cooling oil of claim
 9. 14. Thedevice of claim 11, wherein the device is at least one selected from thegroup consisting of a motor, a battery, an inverter, an engine and anelectric cell.
 15. The base oil of claim 3, wherein a thermalconductivity of the base oil at 25 degrees C. is 0.142 W/(m·K) or more.16. The base oil of claim 3, wherein a volume resistivity of the baseoil at 25 degrees C. is 10¹⁰ Ω·cm or more.
 17. A device-cooling oil,comprising the base oil of claim
 3. 18. A device configured to be cooledby the device-cooling oil of claim
 17. 19. The device of claim 18,wherein the device is suitable for an electric vehicle or a hybridvehicle.
 20. The device of claim 18, wherein the device is at least oneselected from the group consisting of a motor, a battery, an inverter,an engine and an electric cell.
 21. A device cooling method comprisingcontacting a device with the device-cooling oil of claim
 17. 22. Thedevice of claim 19, wherein the device is at least one selected from thegroup consisting of a motor, a battery, an inverter, an engine and anelectric cell.
 23. The base oil of claim 5, wherein a thermalconductivity of the base oil at 25 degrees C. is 0.142 W/(m·K) or more.24. The base oil of claim 5, wherein a volume resistivity of the baseoil at 25 degrees C. is 10¹⁰ Ω·cm or more.
 25. A device-cooling oil,comprising the base oil of claim
 5. 26. A device configured to be cooledby the device-cooling oil of claim
 25. 27. The device of claim 26,wherein the device is suitable for an electric vehicle or a hybridvehicle.
 28. The device of claim 26, wherein the device is at least oneselected from the group consisting of a motor, a battery, an inverter,an engine and an electric cell.
 29. A device cooling method, comprisingcontacting a device with the device-cooling oil of claim
 25. 30. Thedevice of claim 27, wherein the device is at least one selected from thegroup consisting of a motor, a battery, an inverter, an engine and anelectric cell.
 31. The base oil of claim 6, wherein a thermalconductivity of the base oil at 25 degrees C. is 0.142 W/(m·K) or more.32. The base oil of claim 6, wherein a volume resistivity of the baseoil at 25 degrees C. is 10¹⁰ Ω·cm or more.
 33. A device-cooling oil,comprising the base oil of claim
 6. 34. A device configured to be cooledby the device-cooling oil of claim
 33. 35. The device of claim 34,wherein the device is suitable for an electric vehicle or a hybridvehicle.
 36. The device of claim 34, wherein the device is at least oneselected from the group consisting of a motor, a battery, an inverter,an engine and an electric cell.
 37. A device cooling method, comprisingcontacting a device with the device-cooling oil of claim
 33. 38. Thedevice of claim 35, wherein the device is at least one selected from thegroup consisting of a motor, a battery, an inverter, an engine and anelectric cell.